The present invention generally relates to a microwave plasma source in which a high frequency discharge in a magnetic field is made use of and which finds applications in a microwave plasma etcher, a plasma depositer and others. In particular, the present invention concerns the microwave plasma source which exhibits an improved performance or operability upon switching from a plasma ignition phase to a normal ion extraction phase.
As an ion source apparatus capable of extracting a high ion current which is required for ion implantation and ion beam deposition in the semiconductor industry, there is disclosed in U.S. Pat. No. 4,058,748 a typical microwave plasma source apparatus in which a high frequency discharge in a magnetic field is made use of. In this known microwave plasma source apparatus, however, the magnetic field intensity required for ignition of plasma differs at a ratio of about 10/6 from the magnetic field intensity required usually for ion extraction which takes place in succession to the plasma ignition phase or mode. As the consequence, operation for readjusting the value of magnetic field intensity is indispensable upon transition from the plasma ignition phase or mode to the ion extraction phase or mode. More specifically, the magnetic field of high intensity set for the plasma ignition mode has to be readjusted to a magnetic field of low intensity for the ion extraction mode through a dial operation which is not only a troublesome procedure but also accompanied with the possibility of erroneous operation. Under the circumstance, there has been a demand for improvement in this respect.